With the advent of multi-channel audio technology for movie soundtracks encoded in formats such as DTS, DOLBY DIGITAL®, DVD Audio, DVD-A, Super Audio Compact Disc, SACD, or the like, surround-sound speakers capable of producing wide dispersion output have been in increasingly high demand for both auditorium and home theatre applications. Surround speaker requirements include diffuse dispersion in the horizontal axis to blur the time arrivals to the listener's ear. This concept is referred to as “reverb.” The audio source may be music, a sound effect, or the like. Multiple speakers can be grouped together to provide a wide dispersion of sound, but there is a nontrivial likelihood that the interaction between such acoustic sources will be acoustically destructive, degrading the sound quality heard by a listener.
Ideally, a point source solution is the answer to this difficulty, but due to size limitations (i.e., most compression drivers are roughly cylindrical with diameters between about 5 and 8 inches, making close placement difficult) and limitations of power output capabilities, such a design is impractical and unfeasible in most working applications. Accuracy and intelligibility of acoustic signal is a result of the way the loudspeaker reconstructs the temporal and spectral response of the reproduced wave front. Phase coherence of the signal or wave front is a result of the temporal response when reconstructed. A number of difficulties arise when attempting to sum acoustic wavefronts from multiple drivers including standing waves interference and phase cancellation between mutually acoustic sources.
In practice, the surround-sound speaker design has generally been approached by providing a bi- or tri-polar speaker with 180 degrees dispersion in the horizontal axis. The difficulty with this design is that most transducers tend to narrow the dispersion angle as the wavelength of the output increases to beyond the area of the transducer mouth. This effect is referred to as “beaming”. The waveguide geometry and/or the throat dimension of the compression driver and/or the diaphragm area of a dome tweeter are the primary contributors to beaming. To avoid beaming, multiple transducers can be used in an arc or array to maximize the dispersion angle in the horizontal axis. Unfortunately, the complication in this approach is that the polar patterns of dispersion tend to overlap or mesh, and thus do not sum acoustically in the axis wherein the transducers are placed due to phase differences. The phase differences give rise to destructive interference, which is interpreted by the listener as a reduction in fidelity and sound quality. Therefore, beaming is reduced at the expense of sound quality from incoherent phase contributions.
Thus, there remains a need for a surround-sound speaker design that can provide surround-sound without both beaming and destructive interference from the horns. The present invention addresses this need.